Trojan horse

American  

[troh-juhn hawrs] / ˈtroʊ dʒən ˌhɔrs /

noun

1. Classical Mythology. a gigantic hollow wooden horse, left by the Greeks upon their pretended abandonment of the siege of Troy. The Trojans took it into Troy and Greek soldiers concealed in the horse opened the gates to the Greek army at night and conquered the city.

2. a person or thing intended to undermine or destroy from within.

3. Also called Trojan.  Computers. a nonreplicating computer program planted illegally in another program to do damage locally when the software is activated.

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Trojan Horse British  

noun

1. Also called: the Wooden Horse.  Greek myth the huge wooden hollow figure of a horse left outside Troy by the Greeks when they feigned retreat and dragged inside by the Trojans. The men concealed inside it opened the city to the final Greek assault

2. a trap intended to undermine an enemy

3. computing a bug inserted into a program or system designed to be activated after a certain time or a certain number of operations

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Trojan Horse Cultural  

1. In classical mythology, a large, hollow horse made of wood used by the Greeks to win the Trojan War (see also Trojan War). The resourceful Odysseus had come up with the plan for the horse. The Greeks hid soldiers inside it and left it outside the gates of Troy. They anchored their ships just out of sight of Troy and left a man behind to say that the goddess Athena would be pleased if the Trojans brought the horse inside the city and honored it. The Trojans took the bait, against the advice of Cassandra and Laocoon. That night the Greek army returned to Troy. The men inside the horse emerged and opened the city gates for their companions. The Greeks sacked the city, thus winning the war.

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Discover More

The story of the Trojan horse is the source of the saying “Beware of Greeks bearing gifts.”

Etymology

Origin of Trojan horse

First recorded in 1570–80, in 1835–40 Trojan horse for def. 2, and in 1970–75 Trojan horse for def. 3

Example Sentences

VCRs were a Trojan horse in the American home that kicked off a rebellion against the centralized entertainment of the big three networks and movie-theater chains.

From The Wall Street Journal • Feb. 14, 2026

This so called Trojan horse effect allows harmful pathogens to persist and spread through drinking water systems and may also play a role in the rise of antibiotic resistance.

From Science Daily • Jan. 25, 2026

A "Trojan horse" therapy that sneaks toxic drugs inside cancer cells is being made available on the NHS in England in a world first.

From BBC • Jun. 12, 2025

The plane is not just a hefty bribe, but also—at least potentially—a flying Trojan horse.

From Slate • May 12, 2025

Once the virus enters the cell, it becomes a Trojan horse.

From "The Hot Zone" by Richard Preston